Such rollover protection systems serve to protect the occupants of motor vehicles that do not have a protective roof, typically convertibles or sports cars.
It is known in the art to provide a fixed rollover bar extending across the entire width of the vehicle or to assign a fixed, non-height adjustable, rollover bar to each vehicle seat.
In both of these solutions, the increased air resistance and driving noise as well as the effect on the appearance of the vehicle in the case of convertibles are perceived as drawbacks.
As a result, design solutions in which the rollover bar is normally retracted and is rapidly extended into its protective position in case of danger, i.e. in case of an impending rollover, in order to prevent the vehicle occupants from being crushed by the rolling vehicle, are becoming increasingly prevalent in the market.
These solutions typically have a rollover bar for each seat which is U-shaped or made of structural sections and which is guided in a cassette housing fixed to the vehicle. This rollover bar is normally held in its lower standby position by a holding device against the bias of a compression drive spring. In case of a rollover, the holding device is released, sensor-controlled, to bring the rollover bar into its upper protective position by the spring force. An operatively engaging locking mechanism then prevents the rollover bar from being pushed back into the cassette.
The holding device typically comprises a holding member which is fixed to the rollover bar and which is in releasable operative mechanical engagement with a trigger member on a sensor-controlled trigger system that is typically formed by a trigger magnet, the so-called crash magnet, or by a pyrotechnic trigger member.
The locking mechanism typically comprises a rotatably coupled spring-loaded detent with toothed segments, also referred to as a locking pawl, and a fixed toothed bar, a notched pin or the like. One locking element is connected with the rollover bar while the other is fixed to the vehicle.
Such a cassette construction of a rollover bar protection system is disclosed, for instance, in German Patent Specification DE 100 40 642 C1. A further development of the cassette system is disclosed in German Laid Open Publication DE 43 42 400 A1.
Once the rollover bar has been triggered it is operationally necessary, particularly for testing/inspection purposes, to unlock the system manually and to push the rollover bar manually into the cassette against the force of the preloaded compression drive spring. In the system according to the cited document DE 43 42 400 C2, the locking pawl has an extended lever arm that makes it possible manually to pivot the locking pawl against the force of the preloading spring while the rollover bar is in its extended state and thereby operatively to disengage the locking pawl from the notched pin and to enable the rollover bar to be pushed in manually. The problem is that the two processes must be carried out simultaneously, i.e. the operator has to use one hand to pivot the locking pawl and the other hand to push the rollover bar into the cassette. This pushing-in requires substantial force to compress the strong compression drive springs.
The German Patent Specification DE 199 10 424 C1 discloses a self-holding unlocking mechanism in rollover bar protection systems, which automatically holds the locking pawl in its unlocked position after it has been manually unlocked, so that the rollover bar can be pushed into the cassette with both hands. Once the initial position is reached, it is automatically locked. This prior-art unlocking mechanism is very complex, however. It has a comparatively large number of components, which must be very precisely coordinated with one another.
The same is true for the self-holding unlocking mechanism of the initially described rollover protection system according to the German laid Open Publication DE 100 42 420 A1. For its self-holding action this mechanism has a reversing lever, which is manually brought into a dead center position and which is to be held in this basically unstable equilibrium position by suitable additional means with the aid of positive or frictional locking. This self-holding action can be cancelled depending on the position of the rollover bar by means of a complex tappet/rod system.